components: default the user-defined empty ctor and dtor where possible

I need an owner's approval please for changes under:
components/prefs

This is a mechanical change. There are a few instances (but not all)
of empty user-defined constructors and destructors which can be
defaulted in the /components code.

This CL was uploaded by git cl split.

R=gab@chromium.org

Bug: 371316188
Change-Id: I63c39f2856361e8c805f424a69968251202ce175
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5917418
Commit-Queue: Dominic Battré <battre@chromium.org>
Reviewed-by: Dominic Battré <battre@chromium.org>
Auto-Submit: Sorin Jianu <sorin@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1366028}

components/prefs/in_memory_pref_store.cc

@@ -12,9 +12,9 @@
 #include "base/observer_list.h"
 #include "base/values.h"
 
-InMemoryPrefStore::InMemoryPrefStore() {}
+InMemoryPrefStore::InMemoryPrefStore() = default;
 
-InMemoryPrefStore::~InMemoryPrefStore() {}
+InMemoryPrefStore::~InMemoryPrefStore() = default;
 
 bool InMemoryPrefStore::GetValue(std::string_view key,
                                  const base::Value** value) const {

components/prefs/ios/pref_observer_bridge.mm

@@ -10,7 +10,7 @@
 PrefObserverBridge::PrefObserverBridge(id<PrefObserverDelegate> delegate)
     : delegate_(delegate) {}
 
-PrefObserverBridge::~PrefObserverBridge() {}
+PrefObserverBridge::~PrefObserverBridge() = default;
 
 void PrefObserverBridge::ObserveChangesForPreference(
     const std::string& pref_name,

components/prefs/json_pref_store_unittest.cc

@@ -93,14 +93,14 @@ class InterceptingPrefFilter : public PrefFilter {
   OnWriteCallbackPair on_write_callback_pair_;
 };
 
-InterceptingPrefFilter::InterceptingPrefFilter() {}
+InterceptingPrefFilter::InterceptingPrefFilter() = default;
 
 InterceptingPrefFilter::InterceptingPrefFilter(
     OnWriteCallbackPair callback_pair) {
   on_write_callback_pair_ = std::move(callback_pair);
 }
 
-InterceptingPrefFilter::~InterceptingPrefFilter() {}
+InterceptingPrefFilter::~InterceptingPrefFilter() = default;
 
 void InterceptingPrefFilter::FilterOnLoad(
     PostFilterOnLoadCallback post_filter_on_load_callback,

components/prefs/mock_pref_change_callback.cc

@@ -10,7 +10,7 @@ MockPrefChangeCallback::MockPrefChangeCallback(PrefService* prefs)
     : prefs_(prefs) {
 }
 
-MockPrefChangeCallback::~MockPrefChangeCallback() {}
+MockPrefChangeCallback::~MockPrefChangeCallback() = default;
 
 PrefChangeRegistrar::NamedChangeCallback MockPrefChangeCallback::GetCallback() {
   return base::BindRepeating(&MockPrefChangeCallback::OnPreferenceChanged,

components/prefs/overlay_user_pref_store_unittest.cc

@@ -39,7 +39,7 @@ class OverlayUserPrefStoreTest : public testing::Test {
     overlay_->RegisterPersistentPref(shared_key);
   }
 
-  ~OverlayUserPrefStoreTest() override {}
+  ~OverlayUserPrefStoreTest() override = default;
 
   base::test::TaskEnvironment task_environment_;
   scoped_refptr<TestingPrefStore> underlay_;

components/prefs/persistent_pref_store.h

@@ -37,7 +37,7 @@ class COMPONENTS_PREFS_EXPORT PersistentPrefStore : public WriteablePrefStore {
 
   class ReadErrorDelegate {
    public:
-    virtual ~ReadErrorDelegate() {}
+    virtual ~ReadErrorDelegate() = default;
 
     virtual void OnError(PrefReadError error) = 0;
   };

components/prefs/pref_member.h

@@ -159,12 +159,12 @@ class PrefMember : public subtle::PrefMemberBase {
  public:
   // Defer initialization to an Init method so it's easy to make this class be
   // a member variable.
-  PrefMember() {}
+  PrefMember() = default;
 
   PrefMember(const PrefMember&) = delete;
   PrefMember& operator=(const PrefMember&) = delete;
 
-  virtual ~PrefMember() {}
+  ~PrefMember() override = default;
 
   // Do the actual initialization of the class.  Use the two-parameter
   // version if you don't want any notifications of changes.  This
@@ -274,7 +274,7 @@ class PrefMember : public subtle::PrefMemberBase {
     }
 
    protected:
-    ~Internal() override {}
+    ~Internal() override = default;
 
     COMPONENTS_PREFS_EXPORT bool UpdateValueInternal(
         const base::Value& value) const override;

components/prefs/pref_member_unittest.cc

@@ -62,7 +62,7 @@ class GetPrefValueHelper
 
  private:
   friend class base::RefCountedThreadSafe<GetPrefValueHelper>;
-  ~GetPrefValueHelper() {}
+  ~GetPrefValueHelper() = default;
 
   void GetPrefValue(base::WaitableEvent* event) {
     value_ = pref_.GetValue();

components/prefs/pref_notifier.h

@@ -13,7 +13,7 @@
 // cleaned up all public uses of this interface.
 class PrefNotifier {
  public:
-  virtual ~PrefNotifier() {}
+  virtual ~PrefNotifier() = default;
 
   // Sends out a change notification for the preference identified by
   // |pref_name|.

components/prefs/pref_notifier_impl_unittest.cc

@@ -51,7 +51,7 @@ class MockPrefNotifier : public PrefNotifierImpl {
  public:
   explicit MockPrefNotifier(PrefService* pref_service)
       : PrefNotifierImpl(pref_service) {}
-  ~MockPrefNotifier() override {}
+  ~MockPrefNotifier() override = default;
 
   MOCK_METHOD(void, FireObservers, (std::string_view path), (override));
 

components/prefs/pref_service.h

@@ -108,7 +108,7 @@ class COMPONENTS_PREFS_EXPORT PrefService {
     Preference(const PrefService* service,
                std::string name,
                base::Value::Type type);
-    ~Preference() {}
+    ~Preference() = default;
 
     // Returns the name of the Preference (i.e., the key, e.g.,
     // browser.window_placement).

components/prefs/pref_service_factory.cc

@@ -19,7 +19,7 @@
 PrefServiceFactory::PrefServiceFactory()
     : read_error_callback_(base::DoNothing()), async_(false) {}
 
-PrefServiceFactory::~PrefServiceFactory() {}
+PrefServiceFactory::~PrefServiceFactory() = default;
 
 void PrefServiceFactory::SetUserPrefsFile(
     const base::FilePath& prefs_file,

components/prefs/pref_service_unittest.cc

@@ -349,7 +349,7 @@ class WriteFlagChecker : public TestingPrefStore {
   bool last_write_flags_set() { return last_write_flags_set_; }
 
  private:
-  ~WriteFlagChecker() override {}
+  ~WriteFlagChecker() override = default;
 
   void SetLastWriteFlags(uint32_t flags) {
     CHECK(!last_write_flags_set_);

components/prefs/pref_store_observer_mock.cc

@@ -11,7 +11,7 @@
 PrefStoreObserverMock::PrefStoreObserverMock()
     : initialized(false), initialization_success(false) {}
 
-PrefStoreObserverMock::~PrefStoreObserverMock() {}
+PrefStoreObserverMock::~PrefStoreObserverMock() = default;
 
 void PrefStoreObserverMock::VerifyAndResetChangedKey(
     const std::string& expected) {

components/prefs/pref_value_map.cc

@@ -14,9 +14,9 @@
 
 #include "base/values.h"
 
-PrefValueMap::PrefValueMap() {}
+PrefValueMap::PrefValueMap() = default;
 
-PrefValueMap::~PrefValueMap() {}
+PrefValueMap::~PrefValueMap() = default;
 
 bool PrefValueMap::GetValue(std::string_view key,
                             const base::Value** value) const {

components/prefs/pref_value_store.cc

@@ -70,7 +70,7 @@ PrefValueStore::PrefValueStore(PrefStore* managed_prefs,
   CheckInitializationCompleted();
 }
 
-PrefValueStore::~PrefValueStore() {}
+PrefValueStore::~PrefValueStore() = default;
 
 std::unique_ptr<PrefValueStore> PrefValueStore::CloneAndSpecialize(
     PrefStore* managed_prefs,

components/prefs/value_map_pref_store.cc

@@ -66,7 +66,7 @@ void ValueMapPrefStore::SetValueSilently(std::string_view key,
   prefs_.SetValue(key, std::move(value));
 }
 
-ValueMapPrefStore::~ValueMapPrefStore() {}
+ValueMapPrefStore::~ValueMapPrefStore() = default;
 
 void ValueMapPrefStore::NotifyInitializationCompleted() {
   for (Observer& observer : observers_)